Traumatic Brain Injury (TBI) is the leading cause of death and disability in children and, among those under age 15, TBI results in an estimated 2,685 deaths, 37,000 hospitalizations, and 435,000 ED visits annually in the U.S. Fortunately, there is growing evidence that the management of TBI in the early minutes after injury may profoundly impact outcome. This has led to the promulgation of evidence-based TBI treatment guidelines by authoritative national and international scientific bodies. Reports on guideline implementation in the hospital setting are very promising. However, no studies have evaluated their impact in the prehospital setting in either children or adults. While randomized prehospital trials to identify the effectiveness of the guidelines would clearly be optimal, the strong indirec evidence currently precludes withholding guideline therapy because of ethical considerations. Thus a large, prospective, historically-controlled, observational study carried out across diverse EMS systems is the best methodology currently available to evaluate the effectiveness of implementing the guidelines in the prehospital setting. --Specific Aim: To test the hypothesis that implementation of the TBI guidelines in a statewide EMS system will reduce mortality and improve non-mortality outcomes in children less than age 18 with severe TBI. --Objective #1: Implement the internationally-vetted TBI guidelines across a broad variety of EMS systems (urban/suburban/rural) throughout Arizona. This will be accomplished through the statewide collaboration between the University of Arizona, the Arizona Department of Health Services, and local EMS agencies responding to 85% of the population. This will mirror the approach that has been successfully employed to study and document a tripling of patient survival from out-of-hospital cardiac arrest in the state. --Objective #2: Collect prehospital EMS and trauma center data on children with severe TBI cared for by participating EMS agencies to determine pre-implementation and post-implementation injury severity/risk- adjustment measures and outcomes. --Objective #3: Evaluate the impact of prehospital guideline implementation on the following outcomes: 1) Survival among all severe cases and among patients who are incubated prior to hospital arrival and 2) non- mortality outcomes such as hospital/ICU length of stay, ventilator days, and patient disposition. --Relevance/health impact: The societal burden of TBI is immense and this is especially true among the young. While the potential for improving survival through early intervention appears to be great, the effectiveness of the prehospital guidelines remains unproven. Demonstrating improved outcomes from TBI guideline adoption would potentially lead to widespread implementation throughout the U.S. and significant reduction of morbidity and mortality from this major public health problem. If, on the other hand, this study demonstrates that the TBI guidelines do not improve outcomes, despite systematic implementation across a wide variety of EMS systems, such evidence would provide the ethical basis for conducting randomized prehospital trials in the future. PUBLIC HEALTH RELEVANCE: The impact of Traumatic Brain Injury (TBI) on society is enormous and this is especially true among the young. In fact, TBI is the leading cause of death and disability in children and, among those under age 15, TBI results in an estimated 2,685 deaths, 37,000 hospitalizations, and 435,000 ED visits annually in the U.S. Authoritative scientific bodies have promulgated evidence-based TBI treatment guidelines and the potential for dramatically reducing morbidity and mortality from TBI by implementing these internationally-vetted guidelines in the prehospital setting appears to be great. However, the effectiveness of these guidelines remains unproven for care delivered outside of the hospital. Validating the impact of these treatment guidelines in Emergency Medical Services systems would potentially lead to widespread implementation and, thereby, reduce morbidity and mortality from this immense public health problem.